This invention concerns a push button switch, particularly, a master, or power, switch, having: housing-affixed contacts and at least one contact bridge for bridging the contacts that is movable by means of a spring plunger; an over-center spring-switching mechanism that is operatively coupled between the spring plunger and a manually-movable sliding switch; and a sliding locking linkage for the sliding switch for alternately locking the sliding switch in the "on" and "off" positions.
Such switches are often used for controlling electrical power to consumer appliances, particularly television-like devices.
German Auslegeschrift DE-AS 1 590 503 discloses such a push button switch. Experience has shown that such push button switches, in spite of their over-center spring switching mechanisms, can be manipulated in undesirable manners so that contact pressures are thereby influence. If, in such a switch, a switch button is not moved quickly enough, that is, it is moved very slowly and/or is only partly shoved in, in spite of its over-center spring switching mechanism, it can happen that a contact pressure of a contact bridge lying on housing-affixed contacts will go to zero and this condition can be maintained manually. This creates an increase in contact resistance and consequently produces contact heating. An increase in contact wear is associated therewith. Further, an overheated push button switch can result whose functioning ability as well as life span is not only decreased but which also presents a fire hazard.
A similar push button switch is described in German Gebrauchsmuster DE-GM 91 01 126. With the device described in this publication a contact vibration, or bounce, is avoided. However, this switch also has the above described problems.
German Offenlegungsschrift DE 31 50 046 A1 describes a push button switch in which partially welded contacts are supposedly torn open by means of a separating mechanism. The above described problems are not overcome by this device.
In German Offenlegungsschrift DE 28 39 108 A1 a button snap switch is disclosed. In this device, a sliding switch must be moved in different directions for turning it on and off. In the switch of German Offenlegungsschrift DE 28 39 108 A1 arcs and contact vibrations are supposedly prevented. In this device, a latching apparatus is provided which blocks a spring plunger in its two end positions and which is releasable by movement of the sliding switch. However, undesired manipulations are possible with this switch which cause the above mentioned problems to occur.
Another push button switch is described in German Offenlegungsschrift DE 20 31 364 A1. Also, in this device a sliding switch does not alternately engage upon each pushing thereof in "on" and the "off" positions. In order to achieve a snapping operation, a member coupled to a snapping spring is shoved over a cam.
German patent DE 36 44 437 C1 discloses a push button switch with an interengaging apparatus having a detent, or groove, and an engaging finger as a locking apparatus. In order to compensate for undue demands placed on its manipulated member in an activation direction, the locking apparatus is held by means of a spring in a shiftable position.
It is an object of this invention to provide a push button switch of the type mentioned in the first paragraph of the "BACKGROUND OF THE INVENTION" above in which an improper manual manipulation cannot easily lead to increased wear and to operational uncertainty.